The purposes of the project are to determine the effects of abnormal glucose tolerance on outcome of the pregnancy, to determine long term prognosis for the women and their offspring, and to identify diabetes and impaired glucose tolerance during pregnancy in women in the Gila River Indian Community. By means of a glucose tolerance test as well as chart review, the diabetes status of every woman is determined at two-yearly intervals and during the third trimester of each pregnancy. Offspring are followed from age 5 years and the effects of the diabetic intrauterine envrionment are evaluated in conjunction with other risk factors for obesity and diabetes. Pima Indians who had been breast fed as infants were found to have lower rates of non-insulin-dependent diabetes than those who had not been breast fed. To explore other possible consequences of this breast feeding, the effect of having been breast fed in infancy on glucose concentration during pregnancy was examined. Glucose concentration was measured after a 75g oral glucose load in 93 Pima women aged < 25 years who, as infants, had been breast fed for greater than or equal to 1 month and 88 who had not. When controlled for other factors influencing glucose tolerance (age, BMI, birth weight, diabetes in greater than or equal to 1 parent, and maternal diabetes during pregnancy), the mean 2-h plasma glucose concentration was lower in pregnant women who had been breast fed (5.7 mmol/l vs 6.3 mmol/l, p=0.034). Thus, breast feeding, which is associated with less diabetes in nonpregnant Pima Indians, is also associated with lower plasma glucose concentrations during pregnancy. Seventeen of 73 women who were pregnant and 114 of 244 women who were not pregnant when IGT was recognized developed diabetes within 10 years. Controlled for glucose concentration, age, body mass index, parity and duration of follow-up, those who were not pregnant were at higher risk of diabetes than those who were pregnant (odds ratio=1.71, 95% confidence interval=1.01-2.91). This study suggests that, during pregnancy, although women with IGT are at a higher risk of diabetes than women with normal glucose tolerance, they are at lower risk than non-pregnant women with a similar glucose concentration who, in the clinical setting, are likely to remain unrecognized.